A method and an arrangement of this kind are disclosed in U.S. patent application Ser. No. 08/836,018, filed Apr. 29, 1997, now U.S. Pat. No. 5,880,568. There, a control unit is provided which includes a microcomputer. The microcomputer carries out the control of the power of the drive unit (in the case of an internal combustion engine, via air supply, fuel metering and/or ignition angle) as well as the monitoring of the correct function of these control programs. The program structure of this microcomputer includes essentially three mutually separated levels (compare also the description with respect to FIG. 1). In a first level, the control functions are computed. In a second level, the correct operation of the control functions of the first level is checked based on selected input and output signals. In a third level, a check of the monitoring carried out in the second level is realized in the context of a sequence control. This sequence control checks the correct processing of the monitoring steps in cooperative relationship with a monitoring module (watchdog or safety computer). For this purpose, the monitoring module poses a question, which is selected from predetermined questions. This question is answered by the second level by forming a part answer of the programs. The second level sends the question back to the monitoring module for detecting faults. In the preferred embodiment, the second level monitors the air adjustment of the engine and, in the case of a fault, switches this air adjustment off or initiates an emergency operation. In this embodiment, the monitoring module intervenes in the output stage for the actuator, which controls the air supply, as well as in the output stages for the metering of fuel and in the ignition. Measures for monitoring the computations, which are carried out in the context of the function monitoring in the second level, in addition to the control of the program sequence are not described in this known solution.
It is an object of the invention to provide measures for checking the computations in the context of the function monitoring.